This invention relates to a semiconductor light-emitting device, more particularly to a blue light emitting semiconductor laser.
Conventional semiconductor lasers have a double-hetero structure made of III-V compound semiconductor materials such as In.sub.x Ga.sub.1-x P.sub.y As.sub.1-y /GaAs, Ga.sub.x Al.sub.1-x As/GaAs, In.sub.x Al.sub.1-x P/In.sub.y Ga.sub.1-y P (0&lt;x and y&lt;1), etc. Thus, their emitting wavelength is limited to an infrared region and visible red region.
On the other hand, semiconductor lasers having an emitting wavelength in visible short-wavelength regions will have many advantages, if practically utilized. For example, if a blue light semiconductor laser is utilized for an optical disk, the recording density can be increased. A semiconductor laser of ultraviolet region over to the green region can make the sensitivity of an optical printer higher. Further, plastic optical fibers, which are regarded as important in short-distance communications, have a high loss in the infrared region and have a low-loss region at about 550 nm. Thus, green light semiconductor laser has been regarded as an important light source for short-distance communications. Furthermore, ultraviolet light semiconductor laser could be applied as a light source for phosphor excitation or as a light source for process technique using light-sensitive materials or as an experimental light source. Thus, visible light semiconductor lasers having a shorter wavelength than 0.5 .mu.m band have many advantages and their practical application have been keenly desired.
As the semiconductor lasers emitting light in the blue region, Japanese Patent Unexamined Publication (JP-A) No. 60-178684 discloses a semiconductor laser having a double-hetero structure, wherein a four-component mixed crystal system of ZnS.sub.x Se.sub.y Te.sub.1-x-y (0.ltoreq.x, y.ltoreq.1) is used as an active layer.
Japanese Patent Unexamined Publication (JP-A) No. 63-95692 discloses a semiconductor laser having a layer of ZnS.sub.x Te.sub.1-x (0.ltoreq.x.ltoreq.1) sandwiched by p-type and n-type layers of ZnS.sub.y Te.sub.1-y (0.ltoreq.y.ltoreq.1).
A semiconductor laser having a double-hetero structure comprising a ZnS.sub.x Te.sub.1-x layer, both sides of which are formed p-type and n-type layers of ZnS.sub.y Te.sub.1-y, and having an emitting wavelength in the 0.5 .mu.m band resion is disclosed in U.S. patent application Ser. No. 07/469,382, now U.S. Pat. No. 5,801,632.
Further, production of iodine doped n-type ZnCdS thin film and electrical properties thereof are disclosed in Preprint of Lectures in 37th Associated Meeting of Applied Physics vol. 1, p. 200 (Lecture No. 28-p-S-3), 1990.